According to conventional techniques for aligning optical elements in an optical system (e.g., in a telescope), a beam splitter and a retroreflector are used in conjunction with photodetectors to detect any deviation that misaligned optical elements would cause between an input beam and a reflected return beam passing through the system. In order to distinguish the return beam from the input beam, it has generally been necessary in conventional techniques for the input beam to be polarized so that the return beam can be distinguished by its phase change upon reflection.